Hot sand curing of shell molds



HOT SAND (ZURING F SHELL MOLDS Julius M. Bleuenstein,

Detroit, Mich, assignor to Ford Motor Company,

Dearborn, Mich., a corporation of This invention relates to the foundingart and disclosures particularly an improvement in the currentlyutilized methods of preparing shell molds. Due to the fact that patternsfor the formation of shell molds must withstand temperatures in excessof 350 F., they are invariably made of metal. To prepare a shell moldupon such a pattern it is conventional to secure the heated metalpattern to the open upper face of a sand box containing a mixture ofmolding sand of about No. 90 A. F. S. size containing about 7 percent ofa heat settable phenol aldehyde resin. This assemblage of box andpattern is then inverted so that the heated pattern becomes the bottomof the box and the molding sand is dropped upon the hot pattern. Thiscircumstance is allowed to continue for a period of time ranging up to 1minute during which time a layer of the sand resin mixture immediatelyadjacent the heated pattern softens, partially cures and adheres to theheated pattern to form the shell. The heated pattern containing theattached shell is disengaged from the sand box and carried through anoven wherein it is exposed to radiant heat or direct flame to completethe curing of the resin and impart to the mold physical strength.

The instant invention utilizes the same procedure up to the curing stepin the oven. Instead of curing the green mold in an oven, the metalpattern with the attached partly cured mold is again made the upper sideof a second open topped sand box. However, this second sand box isfilled with ordinary sand unmixed with resin but instead heated to atemperature between 350 F. and 1,300 F. After the pattern and mold havebeen secured to the top of this second box, the assemblage is invertedand permitted to remain in this position until the cure has beencompleted by virtue of the heat resident in the hot sand. This sand hasbeen previously heated by direct fire located under the box when it isin the upright position in contradistinction to the inverted position.

It has been found that with an ordinary shell about /a inch thick andwith sand at 900 F. a complete cure may be effected in 15 seconds. Thisis more rapidly than can be done with radiant heat or direct flame andresults in a mold which is more uniformly cured and hence has higherphysical properties.

rates Patent 0 While ordinary sand has been disclosed as the heatcarrying medium and has the advantages of not contaminating molds andbeing readily available, it is to be understood that any thermallystable pulverulent or granular material may be used. Experiments, forexample, with iron shot have shown this material to be even faster thansand of the same temperature but it has the disadvantage of adhering tothe mold. Other materials, such as suitably sized rock particles or ironoxide may obviously be employed as justified by special circumstances.

In the above description where the word mold is used, it

cores as well as molds.

I claim as my invention:

1. The process of preparing shell molds comprising heating a pattern,securing the heated pattern to an open topped sand box containing amixture of sand and a heat settable resin, inverting the assemblage ofsand box and pattern to shower the sand resin mixture upon the heatedpattern, permitting the sand box to remain inverted until a shell of thedesired thickness has been secured, detaching the pattern, carrying theshell from this sand box and attaching it to the top of a'second opentopped sand box containing sand heated to a temperature of 350 F. to1,300 F., inverting the assemblage of the second sand box and patternuntil the desired degree of cure of the resin is obtained, detaching thepattern from the second sand box and removing the shell.

2. The process of preparing shell molds comprising heating a pattern,securing the heated pattern to an open topped sand box containing amixture of sand and a heat settable resin, inverting the assemblage ofsand box and pattern to shower the sand resin mixture upon the heatedpattern, permitting the sand box to remain inverted until a shell of thedesired thickness has been secured, detaching the pattern, carrying theshell from this sand box and attaching it to the top of a second opentopped sand box containing sand heated to a temperature of 350 F. to1,300 E, inverting the assemblage of the second sand box and patternuntil the desired degree of cure of the resin is obtained, detaching thepattern from the second sand box and removing the shell, said second boxbeing heated while in the upright position by direct flame.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES FIAT Final Report No, 1168, PB 81284, May 30, 1947.

is understood that the term is employed to include

